Today, a radar system may be multifunctional, for example both comprising functions for traditional narrowband radar tracking and for broadband electronic warfare (EW). Thus both a radar mode and an EW mode is desired.
In the radar mode, a high output power, and a high degree of efficiency is desired.
In the EW mode, disturbing signals are transmitted, and the transmission should have a very broad bandwidth and linear amplification.
For such a radar system, distributed power amplifiers may be used, where the power amplifiers comprise transistors in so-called wide band-gap (WBG) materials such as gallium nitride (GaN). A distributed amplifier is positioned relatively close to the radar system's radiating elements. The power density for GaN transistors of approximately 400 μm is typically about 7-8 W/mm gate-width compared with about 1 W/mm gate-width for the material gallium arsenide (GaAs). Distributed amplifiers demands small transistors in order to obtain sufficient bandwidth, for example 4-18 GHz, but since it is possible to acquire a relatively high output power from a GaN transistor, a sufficient total output power is obtained anyway.
In order to switch between the radar mode and the EW mode, different arrangements are used today. For example, two different amplifiers with corresponding matching networks may be connected to the same radiating element, where a switch, placed between the amplifiers and an output to a radiating element, switches between the different amplifiers.
Another example comprises one amplifier and two parallel matching networks, where a first switch, placed between the amplifier and the two matching networks switches between the different matching networks. A corresponding second switch is placed between the matching networks and an output to a radiating element. The switches are synchronized, either leading the output from the amplifier to one of the two matching networks, and further to the radiating element, or leading the output from the amplifier to the other matching network, and further to the radiating element.
In the second example, there is one amplifier less, but one more switch. For both these prior art examples, there are problems with high switch losses and isolation between the amplifiers and/or matching networks, and such arrangements also becomes quite large, complex and expensive.
It is therefore desirable to obtain a distributed amplifier arrangement in a radar arrangement having a radar mode and an EW mode, where the drawbacks mentioned above are reduced.